I'm having the same issue running a stock cooler. I'm not sure what's up with this. I'm not overclocking and I reapplied some Arctic Silver Ceramique paste about the size of a pea after I reseated the heatsink thinking it was loose.
I contacted Intel:
nfo: Please wait for a site operator to respond.
info: You are now chatting with 'Victor'
Victor: Hello. Thank you for using the Intel Customer Chat Support service. We are glad to be of service. How may I help you?
: Hello Victor
: My i7-2600k is getting very high temperatures under load
: My heatsink is properly mounted and I re-applied a pea sized amount of TIM
: I ran Prime 95 and the temperature spiked to 80 Degrees Celsius almost immediately
: Then Kept climbing until I stopped the test
: Any ideas? Any numbers on acceptable heat limits?
: I am monitoring the temperature with Realtemp, which I understand is only approximate but it shouldn't be that high based on what I'm seeing online
Victor: the temperatures are indeed high. What are your idle temperatures in BIOS?
: 40 Degrees or so
: I think 35-40 during normal use
Victor: Please provide me the RAM memory part number that you are using.
: It's 16 GB of Gskill Ripjaw memory
: Part number forthcoming...
:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231315
: F3-12800CL9Q-16GBRL
: Memtest passed and I ran PC Check which passed everything
Victor: How are you running the memory in BIOS?
: It's just at 1600Mhz. I'm not overclocking anything
: Although as I understand 1600 Mhz is technically overclocked?
: It is quite a lot of ram
Victor: Yes. And this makes the memory controller on the processor to heat up and also heat up the processor temperature.
: Should I drop it down to 1333?
: I'm not sure how much of a performance difference this really makes
Victor: You should leave it on automatic this way when the Intel(R) Turbo Boost gets enabled it will also increase the memory frequency when needed.
: I'll check that. Any other thoughts?
Victor: Make sure that the fan control on your system is working correctly. Remember to have the latest BIOS installed.
: It's a UEFI system which is kind of a new thing
: I'm not sure if that has anything to do with it
Victor: You can try to get in contact with the manufacturer to see if they have similar reports.
: I mean I know UEFI is new and I've heard it's a bit twitchy but ASUS didn't have anything on it when I called them
Victor: Currently it seems like the issue is with the memory.
: Okay. Is 1066 considered the stock speed?
Victor: 1066/1333 MHz.
: And do you have any specs on what the maximum temp should be? Online I have conflicting information
Victor: It should not go higher than 73°C under heavy load.
: I ran another load tester and I'm getting 50 Degrees C under 100% load
: Just seems strange. Thank you very much for all your help
: I'll try adjusting it down to automatic with 1333 as the starting point in my EFI/BIOS
Victor: You are welcome and thank you for contacting Intel Customer Support.
Re-Ran Prime 95 and while it took longer to hit 90 Degrees it still happened. I went all the way down to 1066. Motherboard is an ASUS Maximus IV Extreme BIOS Rev. 1303. I'm at a loss. Heatsink is definitely attached, verified that the clip pins are held in place on the back of the board...